1. Field of the Invention
The present invention relates to hydroxy ester resins; curable compositions prepared from such hydroxy ester resins; and articles prepared from such curable compositions.
2. Description of Background and Related Art
Hydroxy ester resins such as vinyl ester resins are known in the art and are useful in various enduses including as a binder resin for glass, carbon and polymer fiber composites. Typically, binder resins useful for composites and based on vinyl ester resins derived from conventional epoxy resins such as aromatic glycidyl ethers contain as much as 90 wt % of an unsaturated monomer such as styrene in order to obtain a solution having an adequate viscosity (e.g. between 500 mPa-s and 6,500 mPa-s at 25° C.) in order to be able to use the solution in the process of making composites. For example, U.S. Pat. No. 3,066,112 describes the preparation of various vinyl ester resins from conventional epoxy resins and (meth)acrylic acids. However, the conventional epoxy resins used to prepare the vinyl ester resins known in the art have a high viscosity (for example, greater than 5,000 mPa-s at 25° C.), which in turn makes a vinyl ester resin product having the same high viscosity. Thus, the resultant vinyl ester resin product requires dilution, in order to lower the product's viscosity, before the product can be used as a binder resin.
In addition, problems are encountered when prior art vinyl ester resins made from conventional epoxy resins are used to form a curable composition; and when such curable compositions are cured to form a thermoset. For example, when greater than 10 wt % of prior art vinyl ester resins made from conventional epoxy resins are used as a binder resin to form a curable composition; and when such curable composition is cured to form a thermoset, the resulting thermoset does exhibit a sufficiently high heat resistance as required for some enduses such as for making composites. A cured composite known in the prior art that has a high heat resistance in terms of glass transition temperature (Tg) is a cured composite that exhibits, for example, a Tg greater than about 140° C.
Also, while some known vinyl ester resins based on conventional aliphatic epoxy resins can have a viscosity of less than 5,000 mPa-s at 25° C., the resulting cured composite made from curing these known vinyl ester resins do not maintain a high heat resistance after curing (e.g., Tg greater than about 140° C.).
It is also known that hydroxy esters of carboxylic acids such as acrylic acid and methacrylic acid can be prepared by reacting acrylic acid or methacrylic acid with 1,2-alkylene oxides in the presence of a nitrogen-containing base which serves as a catalyst in the reaction. For example, U.S. Pat. No. 3,987,090 (“the '090 patent”) discloses the preparation of hydroxy esters of acrylic and methacrylic acids and 1,2-alkylene oxides; and an inhibitor R—NO2 (nitrite, R—O—N═O) is used to stabilize the acrylic and methacrylic acids. The '090 patent also describes reactions carried out at elevated reaction temperatures (for example, 80° C.-120° C.) in order to obtain reasonable rates of reaction (epoxide conversion greater than 90% after 8 hours). However, when this known reaction is carried out at the above elevated temperatures a so-called “popcorn” polymerization of the acrylic or methacrylic acids occurs (e.g., undesirable yields of insoluble (meth)acrylic acid polymer are formed) resulting in (i) a significant loss of starting material (e.g., 30% to 100% loss of acrylic or methacrylic acids), and (ii) the undesirable production of an insoluble polymer that may clog a reactor utilized for carrying out the reaction.
It is also reported in the '090 patent that the “popcorn” polymerization problem can be avoided to a large extent by utilizing lower reaction temperatures (e.g., 45° C. to 80° C.). However, as reported in the '090 patent, when the above reaction is carried out at lower reaction temperatures, the rates of reaction are so slow (less than 90% epoxide conversion after 24 hours to 36 hours); the process is not economically feasible.
WO 9856500 discloses the use of C3-C60, substituted or unsubstituted, straight or branch-chained, alkyl, aryl, or aralkyl carboxylate Cr(III) salts, preferably Cr(III) octoate, as catalysts for the reaction of ring systems, such as aziridines, oxiranes, oxetanes and thiiranes with carboxylic acids, anhydrides, lactone and carbonate esters. The reactions described in WO 9856500 are performed at 70° C. to 100° C., and at catalyst concentrations in the range of 4 wt % to 10 wt %. In the case of acrylic and methacrylic acid derivatives, when the Cr(III) catalyst is used, as described in WO 9856500, the catalyst adversely reacts with the olefinic starting material and polymerizes the reactant.